Steve Bannon has lashed out at Republican leaders who failed to support Roy Moore amid a sexual harassment scandal, saying "there is a special place in place for hell" for those who do not back the Alabama Senate candidate.
Mr Moore – a former Alabama state judge with strong support among evangelical conservatives – is standing against Democratic nominee Doug Jones in what is forecast to be a nail-biting vote.
The race for the seat vacated by Jeff Sessions when he became Attorney General has taken on national importance because a Democrat victory would reduce an already slim Republican majority in the chamber to only two seats.
On the eve of the 12 December vote, Mr Bannon took aim at Senate Majority leader Mitch McConnell, former Secretary of State Condoleezza Rice and Tennessee Senator Robert Corker at a campaign rally.
"Mitch McConnell and Senator Shelby, and Condi Rice and all that, little Bobby Corker, all the establishment out there doesn't have Trump's back at all," he told the crowd.
"There's a special place in hell for Republicans who should know better."
The Breitbat chairman's remarks are an apparent gibe at Ivanka Trump, who after the allegations against Mr Moore surfaced last month said “there’s a special place in hell for people who prey on children".
"I’ve yet to see a valid explanation and I have no reason to doubt the victims’ accounts,” she told the Associated Press.
Seven women have accused the Alabama candidate of making unwanted sexual advances when they were underage teenagers and Mr Moore was in his thirties. One of the women claims she was 14 years old at the time she was sexually assaulted.
Another woman claims he judge tried to rape her after offering her a ride home from her job as a waitress.
Mr Moore denies the allegations against him, calling them a "witch hunt".
A number of Senate Republicans have called on Mr Moore stand down from the race, but he has refused.
Mr Trump has given his support to the Alabama Senate candidate, saying the former Alabama justice "totally denied" the allegations against him and telling White House reporters they "have to listen to him, also".
The President boosted Mr Moore's campaign on Saturday, saying: “Get out and vote for Roy Moore. Do it. Do it. We cannot afford, the future of this country cannot afford to lose the seat,”
Mr Trump has struggled to get legislation passed the Senate, where he has a thin 52-48 advantage.
If Mr Moore wins the vote, he is expected to face an investigation by an ethics committee.
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